1. Preheat oven to 180°C/350°F2. Beat butter, extract, sugar and ground almonds in a small bowl with an electric mixer until light and fluffy. Beat in egg; stir in sifted flour.3. Mix rind into jam.4. Roll tablespoons of mixture into balls, place about 5 cm apart on trays, flatten slightly. Indent with the end of a wooden spoon. Fill each hole with jam.